<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="jquery-3.7.1.min.js"></script>
</head>
<body>

<ul>

    <li>abc</li>
    <li>xyz</li>
    <li>china</li>
    <li>fujian</li>
</ul>

<script>

    let map = $('li').map(function (index, e) {
        // console.log(index + ":" + e);
        return $(e).html().toUpperCase();
    });

    console.log(map.get(0));
    console.log(map.get(1));
    console.log(map.get(2));
    console.log(map.get(3));

</script>

</body>
</html>